Service water (i.e. water produced by local water utilities) that is employed for personal, commercial and industrial use typically contains hard water components such as di- and trivalent cations including calcium, magnesium, iron, manganese, copper, etc. The hardness components in service water can have a negative impact on many household, commercial and industrial products and processes using service water. The appearance or utility of swimming pools, lawn care chemicals, laundry compositions, warewashing components, food service preparation, boiler operations, and others can have a negative impact caused by the presence of hardness components in water. In such products and processes, the hardness cations can cause film and scale formation, can interact with and reduce the cleaning capacity of components of cleaning compositions, and can form objectionable precipitates from process by-products. In order to reduce or eliminate such interference caused by hardness components in industrial products and processes, sequestering (chelating) or threshold agents can be used to reduce the interference by adding such agents to the service water separately or as a component of a treatment composition. Sequestering or chelating agents commonly react with the hardness components and prevent potential interaction between the hardness ion and the processes or components used in the processes.
Threshold agents are typically added at very low concentrations, compared to stoichiometric chelating amounts, for the purpose of substantially delaying the formation of hardness precipitates. Threshold agents are typically not used in stoichiometric amounts and typically are compositions that inhibit or poison crystal growth or formation.
Commonly water treatment or chelating agents fall within well known classes of compounds including condensed phosphates, organic phosphonates, organic polycarboxylates, and organic graft copolymers. Condensed phosphates such as alkali metal tripolyphosphates, alkali metal hexametaphosphates, alkali metal pyrophosphates, and others are powerful hardness sequestrants, however due to adverse ecological effects created by the disposal of these phosphates in waterways, non-phosphate chelating agents have been developed and used (see, for example, U.S. Pat. No. 3,308,067, which discloses a number of polycarboxylates useful as chelating agents). Phosphonate chelating agents are equally useful but suffer the same drawbacks. The nonphosphate chelating agents including polycarboxylates and other graft copolymers represent relatively effective replacements for phosphates.
A known class of graft copolymers is disclosed in Knopf et al, U.S. Pat. No. 4,528,334, assigned to Union Carbide Corporation. A review of Knopf as a whole including the preferred reaction temperatures and the Examples shows that the disclosure in Knopf is directed to a specific type of graft copolymer. A primary example of this graft copolymer is shown in Example I of the patent. The Example describes a graft polymerization reaction product of polyalkylene oxide composition and acrylic acid at 150.degree. C. in the presence of an initiating catalyst. Our duplication of the Knopf product indicates that according to the disclosures in the specification and Examples of Knopf, the product is a water insoluble solid or semi-solid. From our characterization work of the polymer product, we have concluded that the insolubility of the semi-solid or solid reaction product relates to its molecular conformation which is a "ladder" polymer.
By a ladder polymer we mean a polymer wherein each ladder side rail, which would correspond to the vertical aspect of the ladder, comprises a polycarboxylate, preferably polyacrylate polymer component and the horizontal or tread portion of the ladder would comprise a polyalkylene oxide. We believe that the insolubility of the Knopf polymer reaction product results from the formation of "side rails" at both ends of the polyacrylate "treads" which reduces the availability of carboxylate moieties to the bulk aqueous phase.
The polymer conformation that we have found in the Knopf materials is a result of the reaction conditions disclosed in the patent and its Examples. Knopf indicates at column 4, lines 3-9 that preferred reaction temperatures range from about 130.degree.-150.degree. C. We have found that these reaction temperatures cause the nearly exclusive formation of the ladder type polymer configuration.
In addition a manufacturing technique in which the chelating agent can be readily manufactured in concentrated form, i.e. does not require the removal of solvent from the concentrated product, is desired. Accordingly, a substantial need exists for a highly effective phosphate-free chelating agent which is readily manufactured and available in a concentrated form.